1. Field of the Invention
The present invention generally relates to a process for producing high purity magnetite from hematite, and a high purity magnetite product formed from the process thereof. Specifically, the invention relates to a process of reducing powdered hematite into magnetite with methane or natural gas, wherein the hematite is reduced in a heating device by a counter-current or concurrent flow of the methane or natural gas, while holding the solids for a specific time at a temperature to effect the reduction to magnetite. The invention further relates to a heating device for performing the method of the invention.
2. Description of the Prior Art
It has been known for many years to convert hematite, composition Fe2O3, into magnetite, composition Fe3O4. Synthetic hematite is a basic reddish brown iron mineral frequently obtained as a byproduct during hydrochloric acid regeneration in operations using this acid to clean or pickle steel products prior to subsequent processing. Synthetic magnetite is utilized for its magnetic and pigmentation properties.
Conversion of hematite into magnetite is known to occur in the presence of hydrogen or carbon monoxide gas or a liquid, wherein the liquid may be petroleum. The hydrogen or carbon monoxide gas or liquid product acts as a reduction agent and reduces the hematite, allowing magnetite to form.
It has been known to spray roast ferrous chloride to produce hematite, pelletize the hematite, and reduce the hematite to magnetite in a heating device at temperatures of about 900° C. to 1000° C. The reduction is performed with carbon monoxide and hydrogen with the flow of reducing gases countercurrent to the flow of hematite pellets which are fed into the reactor opposite a burner flame, and which are heated to greater temperatures as the pellets move through the reactor chamber, attaining maximum temperature near the product discharge. Reducing conditions are preferably maintained throughout the reactor, such as by injection of additional reducing gas into the reactor near the product discharge zone. See for example, U.S. Pat. Nos. 5,348,160 and 5,794,791. No guidance, however, is given as to operating conditions such as gas to solid ratio, flow rates or purity levels
It has also been known to reduce hematite with a reducing gas in the presence of a nonferrous inorganic compound powder at temperatures of about 200 to 700° C., stopping reduction of the powder at about midstream of the reduction to yield a partially reduced powder, and oxidizing a surface of the partially reduced powder with an oxygen-containing gas to yield a composite powder comprising magnetite and iron. The reducing gas can be hydrogen, carbon monoxide, methane or ethane. See, for example, U.S. Pat. No. 6,827,757. The purity for such a process is about 83%.
It has also been known to reduce hematite with organic liquid or low temperature aqueous slurries. See U.S. Pat. Nos. 6,302,952, 5,512,195, 4,376,714 and 3,928,709.
It has also been known in the distant art to reduce hematite with other substances, such as petroleum residue, alcohols and steam, typically at temperatures below 700° C. See for example, U.S. Pat. Nos. 4,311,684, 2,693,409 and 672,192.
In the use of known prior art systems, which require low temperatures, reduction agents that are not methane or natural gas, and which lack guidance as to the amounts of reduction agent to use in relation to the amount of hematite, a purity yield of magnetite from the reduction of hematite is typically in the 80% region, at best. In addition, such processes may require numerous additional steps to perform the reduction properly, which make production on a commercial scale difficult.
There remains, therefore, a very real and substantial need for an improved process to create a high purity magnetite that also presents a process with definite guidelines that are simple, effective and efficient to use, and can further be readily scaled to a commercial scale.